1. Field of the Invention
This invention relates to the remote detection of vibrations of diffuse surfaces, and more particularly to the use of a beam of coherent light which is scattered by the vibration of the diffuse surfaces and then detected as a time-varying intensity distribution.
2. Description of the Prior Art
In the field of covert surveillance, it is often necessary to secretly monitor from a distance conversations, movements of people, and movements of vehicles. As such there exists a need for a novel method and apparatus for the remote detection of such items.
Heretofore, such surveillance has been accomplished by using hidden microphones, interferometers, and microwave equipments. Use of each of these items has presented numerous problems. Hidden microphones, when detected, can be easily destroyed. Interferometers require a visible light wave for operation. In addition extremely precise alignment of the interferometer mirrors is of the utmost importance. Microwave equipments are cumbersome for covert surveillance.